1. Field of the Invention
The present invention relates to flexible highly filled compositions, including highly filled compositions of polymers and elastomers, that may be used in a variety of end-uses, including attenuation of or protection against sound and electromagnetic radiation and as energy conducting materials. The compositions contain at least 90% by weight of filler and are flexible, with a flexural modulus of less than 100 MPa.
2. Description of the Prior Art
Highly filled compositions are capable of being used in a wide variety of applications, especially protection against sound and against electromagnetic radiation and in electrically conductive applications e.g. shielding of apparatus. Examples include mobile flexible X-ray screens, folding X-ray doors, flexible electrical conductors, sound insulating materials, electromagnetic energy screens for apparel e.g. protection against x-rays and beta and gamma radiation, flexible magnets, electrical resistant heating mats and the like, and electrical grounding systems. In some such end-uses, it is important that the material be flexible and resistant against cracking e.g. apparel or containers, whereas in other end-uses it is preferred that the material be rigid e.g. in wall panels or ceiling tiles, or semi-rigid e.g. floor tiles.
A number of filled materials have been proposed for use as protection against radiation. For instance, Japanese patent application No. 58-053928 of K. Yamamoto, published Mar. 30, 1983 discloses an elastic (rubber) foam material, preferably polychloroprene rubber, containing large quantities e.g. 80-87.3% by weight, of metal constituents. The use of lead oxide is disclosed, as well as the use of material containing barium ferrite/nickel ferrite and barium ferrite/magnesium ferrite for protection against magnetism. The compositions also contain minor amounts (&lt;0.5%) of rubber processing aids e.g. magnesium oxide, zinc oxide and lead stearate.
Japanese patent application No. 57-141430 of K. Yamamoto, published Sep. 1, 1982 discloses a leaded foam material comprising a foamed material having as its base a natural or synthetic rubber, preferably polychloroprene rubber, consisting of a mixture of rubber having a molecular weight averaging 20,000 with rubber having a molecular weight ranging from 2,000 to 12,000. 300 or more parts of organic and inorganic lead compounds e.g. lead oxide in amounts of 80-87.3% by weight, are added to 100 parts by weight of the base material. The compositions contain minor amounts (&lt;0.5%) of rubber processing aids e.g. magnesium oxide, zinc oxide and lead stearate.
Canadian Patent 815 609 of J. D. McCluer et al., issued Jun. 17, 1969 discloses a flexible material comprising a fabric base and a layer of lead-loaded elastomeric e.g. polychloroprene, adhering to at least one surface of the fabric base. The lead is in the form of particles of a size smaller than 200 mesh, and constitutes at least 65% by weight of the total weight of the material.
Metal-polymer compositions having an elongation of less than 5% are exemplified in U.S. Pat. No. 3,491,056 of F. L. Saunders et al., issued Jan. 20, 1970.
U.S. Pat. No. 4,379,190 of T. T. Schenck, issued Apr. 5, 1983 discloses compositions of ethylene copolymers and plasticizer that contain 40-90 percent by weight of filler. The fillers exemplified are calcium carbonate and barium sulphate. Related U.S. patents include U.S. Pat. Nos. 4,191,798, 4,263,196 and 4,434,258 all of F. G. Schumacher et al., 4,403,007 of M. C. Coughlin, 4,430,468 of F. G. Schumacher and 4,438,228 of T. T. Schenck.
Japanese patent application No. 61 228 051 of Dainichi Nippon Cables, published Oct. 11, 1986 discloses compositions of ethylene/vinyl acetate and/or ethylene/ethyl acrylate copolymers that contain 5-50 parts of antimony oxide and 5-100 parts of barium sulphate, per 100 parts of polymer, as a wire coating composition. Cross linking of the coated wire with electrons is disclosed.
U.S. Pat. No. 4,563,494 discloses a polymer composition formed from 0.001 to 10% of at least one lanthanide oxide or hydroxide, and organic salts or complexes and a polymer containing e.g. acrylic or methacrylic acid or ester units, for use as a shield against neutron radiation.
U.K. Patents 1 603 654 and 1 603 655, granted Nov. 25, 1981 disclose compositions of metallic lead in polyvinyl chloride as an x-ray absorption material.
Japanese patent application 59 126 296 of Mitsui Petrochemical, published Jul. 20, 1984 discloses the lamination of films of e.g. ethylene/vinyl acetate/carbon monoxide terpolymers onto films of e.g. ethylene/vinyl ester copolymers containing at least 50% by weight of metallic lead, for use in the atomic power industry.
Japanese patent application 57 005 732 of Furukawa Electric Co., published Jan. 12, 1982 discloses compositions of polyolefins e.g. ethylene/vinyl acetate copolymers, containing 30-300 parts, per 100 parts of polymer, of an inorganic powder e.g. barium borate.
Heavy, thick sound insulation using specific low cost barium salts to replace lead compounds is disclosed in Chinese patent application 86004577 of Liu et al. The addition of 100-3000 parts by weight of a metal, metal oxide, metal salts or fillers e.g. iron oxide, ferrite, lead oxide, tin oxide, barium or lead sulphate, barium or lead carbonate, to bituminous or bituminous/rubber compositions is disclosed in Japanese patent application 60 079 065 of Ube Industries, published May 4, 1985. Sound insulating sheet formed by coating iron foil with tin/lead is disclosed in Japanese patent application 60 026 651 of Riken KK, published Feb. 9, 1985.
Compositions of 100 parts of polymers and 20-800 parts of powders of high specific gravity, for use in the manufacture of pipes, are disclosed in Japanese 62 080 031 of Dainichi Nippon Cables, published Apr. 13, 1987. Examples of the polymers are polyethylene, polypropylene and polyvinyl chloride and of the powder are lead, iron, litharge or clay. Japanese 60 213 997 of Toyo Soda, published Oct. 26, 1985 discloses sound insulation formed from 100 parts of polyvinyl chloride, 200-1000 parts of inorganic filler e.g. iron oxides, barium sulphate and lead powder, and plasticizers and thylene/butene-1 copolymers and 600 parts of lead monoxide are exemplified in Japanese 57 158 258 of Hitachi Cable KK, published Sep. 30, 1982.
Japanese Kokai 59 126 296 of S. Madao et al., published Jul. 20, 1984 relates to a laminated composition for shielding against radiation, formed from lead or lead compound in a copolymer resin laminated to plasticized polyvinyl chloride. The copolymer may contain roll releasing agents, blocking inhibiting agents and the like, and the polyvinyl chloride may contain tin maleate and magnesium oxide.
Although the prior art reports compositions of fillers and polymers on a weight basis, the amount of filler on a volume basis is believed to be more important, especially with respect to processing of the compositions. Generally, polymers filled to 5-25% by volume retain a high degree of flexibility, resilience, elongation, elasticity, resistance to flex cracking and the like, whereas polymers filled to 20-50% by volume, if achievable with the aid of plasticizers and suitable combinations of polymers and fillers, tend to be rigid or semi-rigid and brittle and frequently have low resistance to flexing or low tensile strength. In the latter, the polymer is essentially a binder or adhesive for the filler. So-called vinyl floor tiles exemplify highly filled polymer compositions that are generally brittle with low flexibility.
Radiation attenuation materials in the form of mixtures of two or more elements or compounds thereof are disclosed in U.S. Ser. No. 07/440,494 of M. J. Lilley, G. E. Mawdsley, G. P. Reh and M. J. Yaffe, filed Nov. 22, 1989. Radiation protection material, especially apparel, is disclosed in U.S. Ser. No. 07/440,495 of M. J. Lilley, J. M. MacLeod, G. E. Mawdsley, G. P. Reh and M. J. Yaffe, filed Nov. 22, 1989.